This is the traditional text of a wedding invitation, which is typically printed or engraved on special stationery. This is not really intended as a "letter." A separate note for guests to R.S.V.P. is often enclosed.
1234, Main Street
Boston, MA 02123
08 April, 2005
<Recipient Address Goes Here>
Mr. and Mrs. <names> request the honor of your presence as they celebrate the marriage of their daughter, <name> to <name>, son of <names>. The marriage ceremony will take place at <location and address> on <date and time>.
A reception immediately following the ceremony will be held at <location>.
Please join us in celebrating this joyous occasion.
Please R.S.V.P. by <date>.
encl: <List of enclosed items goes here>